1. Field of the Invention
This invention relates broadly to ocular lens devices. More particularly, this invention relates to intraocular lens devices that are surgically implanted within the capsular bag of a human eye as well as other ocular lens devices.
2. State of the Art
Looking at FIG. 1, the natural lens of a human eye is a transparent crystalline body, which is contained within a capsular bag located behind the iris and in front of the vitreous cavity in a region known as the posterior chamber. The capsular bag (or lens capsule) is attached on all sides by fibers, called zonules, to a muscular ciliary body (or process). At its rear, the vitreous cavity, which is filled with a gel, further includes the retina, on which light rays passing through the lens are focused.
Although not to he held to one theory or another, the subject of this invention will be described according to what is know to those skilled in the art as the Helmholtz theory of accommodation (Helmholtz Theory). The Helmholtz Theory states that the lens will change in shape as the lens capsule stretches horizontally and relaxes back to its more rounder geometry. As shown in FIG. 2, when the ciliary muscles are relaxed, the Zonules are under tension causing the lens to stretch horizontally to see far distances. Conversely, as is shown in FIG. 3, when the ciliary muscles are contracted, the Zonules are relaxed and the lens assumes a more rounded shape to enable near vision.
Contraction and relaxation of the ciliary bodies (FIGS. 2 and 3) changes the shape of the bag and of the natural lens therein, thereby enabling the eye to focus light rays on the retina originating from objects at various distances. The ability of the lens to focus both far and near is referred to as “accommodation”. The human eye is subject to a variety of disorders which degrade, or totally destroy, the ability of the eye to function properly. One of the more common of these disorders involves progressive clouding of the crystalline lens matrix resulting in the formation of what is referred to as a cataract. Another is the general hardening of the lens which limits the amount of accommodation of the lens that the zonules and ciliary bodies can impart to the them. The progressive loss of accommodation is called “presbyopia.”
It is common practice to cure a cataract by surgically removing the clouded crystalline lens and implanting an artificial intraocular lens in the eye to replace the natural lens. Various types of intraocular lenses having the capability of altering their refractive power have been suggested in an effort to duplicate the performance of the natural lens within the eye. Such accommodating intraocular lenses, as they are known in the art, have a variety of designs directed to enable the patient to focus on, and thereby clearly see, objects located at a plurality of distances. Examples may be found in such publications as U.S. Pat. Nos. 4,254,509; 4,932,966;  6,299,641; and 6,406,494.
U.S. Pat. No. 5,489,302 discloses an accommodating intraocular lens for implantation in the posterior chamber of the eye. This lens comprises a short tubular rigid frame and transparent and resilient membrane attached thereto at its bases. The frame and the membranes confine a sealed space filled with a gas. The frame includes flexible regions attached via haptics to the posterior capsule. Upon stretching of the capsule by the eye's ciliary muscles, the flexible regions are pulled apart, thereby increasing the volume and decreasing the pressure within the sealed space. This changes the curvature of the membranes and accordingly, the refractive power of the lens.
U.S. Pat. No. 6,117,171 discloses an accommodating intraocular lens which is contained inside an encapsulating rigid shell so as to make it substantially insensitive to changes in the intraocular environment. The lens is adapted to be implanted within the posterior capsule and comprises a flexible transparent membrane, which divides the interior of the intraocular lens into separate front and rear spaces, each filled with a fluid having a different refractive index. The periphery of the rear space is attached to haptics, which are in turn attached to the posterior capsule. Upon stretching of the capsule by the eye's ciliary muscles, the haptics and hence this periphery is twisted apart to increase the volume of rear space and changes the pressure difference between the spaces. As a result, the curvature of the membrane and accordingly, the refractive power of the lens changes.
After surgical implantation of the intraocular lens in the capsular bag of the eye, active epithelial cells on the posterior side of the anterior capsule rim of the capsular bag cause fusion of the rim to the elastic posterior capsule wall by fibrosis. This fibrosis occurs about the haptics of the IOL in such a way that the haptics are effectively “shrink-wrapped” by the fibrous tissue in such a way as to form radial pockets in the fibrous tissue. These pockets contain the haptics with their outer ends positioned within the outer perimeter of the capsular bag. The lens is thereby fixated with the capsular bag with the lens optic aligned with the optical axis of the eye.
With time, depending on the rearward pressure of the intraocular lens on the posterior capsule wall as well as other factors (such as lens material, lens geometry, angulation, sharpness, wrinkles in the posterior capsule wall, etc), epithelium cells can migrate between the posterior capsule wall and the lens and reside and multiply in these spaces. Excessive build up of the cells in this area can lead to opacification of the optic. This opacification, commonly referred to as posterior capsule opacification (PCO), causes clouding of vision and can lead to blurring and possibly total vision loss. The process of PCO is slow and clinical changes often take one to two years to become apparent. PCO is typically treated by YAG laser capsulotomy. However, in terms of health economics, PCO is very expensive to treat.